Agglomerated material in particular for electrical purposes and shaped bodies made therefrom



Patented Nov. 14, 11939 UNETE stares LAB FOR ELECTR HCAL PURPGSES ANDSHAPED BODIES MADE TEEEREFRUM Paul Schwarzkopf, ReuttaAustr-ia NoDrawing. Application June 23, 1937, No. 149,840. in Germany November 28,

i Claims.

This invention relates to an agglomerated ma terial, in particular forelectrical purposes, and shaped bodies made therefrom. The inventionfurther comprises a process of manufacturing such material and bodies.

This application is a continuation in part of my copending applicationSer. No. 681,397, filed July 20, 1933, and issued into Patent No.2,096,- 924 which is in turn a continuation in part of my previouscopending application Ser. No. 594,154 filed February 19, 1932, andissued into Patent No. 2,030,229.

It has been proposed to make such agglomerated material and shapedbodies, in particular for electrical purposes, of different metals, suchas tungsten and molybdenum on one hand and gold, silver, copper, iron,nickel, platinum, aluminum, tin and zinc on the other hand. The highermelting and more refractory metal of the first group in a finelypowdered state as derived from its ores, or compounds, has been mixedwith the lower melting material of the second group, and the latter hasbeen melted so that it compounded with the higher melting material uponcooling.

It has also been proposed to unite tungsten powder by low sintering intoa spongy coherent body, and to cause it to absorb melted copper whichupon cooling fills the pores of the spongy tungsten body.

According to this invention an agglomerated material, in particular forelectrical purposes, and shaped bodies adapted for electrical contactsor the like is also manufactured of metal taken from two groups. Thefirst group consists of tungsten, molybdenum and tantalum which arehighly refractory metals of high melting point and well suited ascontact material. They do not easily melt under the heat of an arcdeveloped between the contacts of a switch when it is opened. They arehowever of low electrical conductivity and oxidize easily when heated tohigh temperature for a more extended period of time. The second group ofmetal comprises silver, copper, nickel, cobalt, iron, gold, chromium,aluminum, tin, zinc, platinum which are of considerably higherconductivity than those of the first group, or which do not oxidize aseasily as the metal of the first group does. In particular, the metalsof the second group do not mix or alloy with those of the first group.

Some of the metals of the second group do not mix under any conditionand some of them do not mix if the metal of the first group remainssolid during agglomeration.

However, according to this invention, the meta bar, or rod,

Serial i931 als of the first group are not taken in the finely powderystate in which they are obtained from their ores or compounds, but areartificially provided with a larger volume in comparison with theirsurface area. In other words,-the metal of the first group is applied inparticles which are coarser than those of the original metal powderobtained from its compounds or ores. By increasing the volume incomparison with the surface area, the resistance against attacks ofoxygen in the surrounding air, also at elevated temperatures, isconsiderably increased. Furthermore, the metal powder is renderedductile and the agglomerated bodies made therewith can be more readilyworked and shaped.

A preferred process of the invention consists in that the tungsten-,molybdenumor tantalumpowder, as it is obtained from the ores orcompounds is first compacted by heat treatment at temperatures at leastas high as sintering temperature whereby a sintered or melted solid bodyof these metals is obtained which is then comminuted to particles of asize coarser than the original metal powder. The sintered or meltedmetal bodies may also be worked, in particular rolled or hammered beforethey are comminuted.

In any case, the coarser particles obtained are more ductile than theoriginal powder, and they are, due to their smaller surface area.compared to the volume enclosed, and due to their larger diameter, moreresistant to corrosion by the electrical arc and the oxygen or the air,if the contacts are heated by the arc The coarse powder thus obtained isuniformly and finely crystalline.

The agglomerated material or shaped bodies may then be made in thefollowing way.

The coarser powder may be mixed with powdery metal taken from the secondgroup and preferably pressed. Thereupon the body is heated to atemperature at which all the lower metal present melts, but below atemperature at which the coarser metal taken from the first group couldchange its structure, in particular soften, sinter or melt.

Thereupon the body is permitted to cool, or cooling is caused in anydesired way, if the structure of the lower melting metal is to beaffected. Pressure may be'applied, if desired, during this, or any otherconsolidation process covered by this invention. The final body may havethe shape of from which the desired contacts or other articles may becut, sliced, or obtained by any other mechanical or even thermaltreatment. (The latter consists in reheating the body into a plastic ormolten state of the lower melting metal contained in the body). Thefinal body however shaped in a suitable mould may already have thedesired shape.

Another process for arriving at the products according to this inventionconsists in shaping the coarser powder taken from the first group and toapply pressure to it, and then to pour over it fused metal taken fromthe second group which infiltrates into the pores of the shaped body ofmetal of the first group and agglomerates upon cooling. Again coolingcan be performed according to any chosen metallurgical rule.

In addition to the metals taken from the first and the second grouptitanium may also be used which is known as a deoxidizing agent. It hasto be present in addition to at least one metal of the first and onemetal of the second group. The amounts of the metal to be taken from thesecond group depend upon the effect desired. The metal of the secondgroup may amount to about 3% to 6% and up to if it has to act merely asa binder, whereas it may be 'present in amounts up to 91%, if it is toact as electrically conducting material in the contact itself.

Titanium, if added, may be used in quantities of about 3% to 6%, up to15%.

The agglomerated body thus obtained has proven in practice to haveexceptional qualities. Due to the presence of tungsten, molybdenum, ortantalum in a coarser state it is more resistant against mechanical wearand deformation during use, for instance as contact in a switch which isto be closed quickly and forcibly. The quasi ductilised coarse particleswill better resist the impact of heavy strokes when the switches" areclosed. Due to the presence of lower melting, but in general betterconducting metal, the contact will not be heated as high by the currentpassing the closed switch as it is the case when tungsten etc. alone isused. Thereby the tendency of the contact to oxidize when the switch isclosed is considerably reduced, because the temperature to which it isheated is lower than it would be if the contact consisted of tungstenetc. alone. Furthermore, such a body can .easily be connected with asupport by soldering at lower temperature, at which the low meltingmetal present can be soldered, whereas soldering of tungsten alone toany support is very difficult, .due to the fact that it is not wetted bymost of the metals. Furthermore, due to the low temperature appliedduring the soldering or brazing operation it can be performed in openair and, in general, without protecting gaseous atmosphere, and nooxidation of the body will occur due to this low temperature and thegreater resistivity of the coarse metal particles against the attacks ofthe oxygen of the surrounding air. The fact that the lower melting metaldoes not mix with the higher melting one is important because the lowmelting metal thus keeps its low melting point and its good brazing andsoldering qualities which would be affected however if an alloy wereformed between that metal and tungsten. Such alloy would be ofconsiderably higher melting temperature lhan that of the lower meltingmetal and the properties of the alloy would essentially diffe from thoseof the low melting component, as far as e. g. soldering and brazingqualities are concerned. I

Even if the low melting metal is not of higher conductivity thantungsten o r molybdenum, as it is the case with tin and zinc, neertheless, the ixirenicly low ll'llillll. point of those metals andtheir low oxidation properties aid in effecting a perfect connectionwith any support in particular of the same metal, excluding anyoxidation of the tungsten particles.

Contacts of this type may be connected with a support of e. g. copper,aluminum, chromium, silver, tin, zinc which may either be rigid, orelastic like springs.

The following examples of binary composite bodies corresponding to theinvention may be given:

Molybdenum-silver; molybdenum-copper; denum-zihc. Tantalum-copper;minum.

Tungsten-silver; tungsten-chromium; tungsten-copper; tungsten-tin;tungsten-zine; tungsten-aluminum.

The following examples of ternary structural composite materials may begiven:

Molybdenum-silver-chromium; molybdenumsilver-titanium;molybdenum-chromium-titanium; molybdenum-chromium-copper;molybdenum-chromium-tin; molybdenum-chromiumzinc;molybdchum-copper-titanium; molybdenum-nickel-COpper.

Tantalum-aluminum-titanium.

Tungsten-silver-titanium; tungsten-chromium-titanium;tungsten-copper-titanium; tungsten-tin titanium; tungsten zinc titanium;tungsten silver chromium; tungsten copper chromium;tungsten-nickel-copper.

For making the material or bodies the process may be to pour the meltedand therefore liquid lower melting metal over the compact high meltingmetal powder. However, parts of the lower melting metal in solid form,more particularly in the form of powder, may be added to and intimatelyadmixed with the powdered higher melting metal, and the whole may thenbe cast over with the remainder of the lower melting metal, which,however, is fused. In this case the whole is preferably maintained at atemperature such that the admixed lower melting metal powder melts aswell and becomes incorporated with the lower melting metal which is caston.

Finally, the procedure may also be such that both the higher melting andlower melting metals are comminuted, mixed and the Whole thereuponheated to such an extent that at least the lower melting metal melts andincorporates the higher melting metal on cooling, which latter willbecome uniformly distributed in the solidified metal.

In these ways in the first place whole blocks or bars can be obtained ofany shape or size, which are homogeneous throughout and from which thedesired article can be made by heat treatment, e. g. recasting, or bymechanical working in the hot or cold, such as hammering, rolling,drawing, cutting, slicing.

The material obtained in this way may be mechanically worked; moreparticularly it may be extended by hammering or rolling and the sheetsobtained punched and pressed.

It is also possible to obtain the desired article direct by insertingthe metal powder mixture into a suitable mould and bringing the lowermelting metal portion in it to fusion so that it takes up the highermelting metal part during cooling and imparts great homogeneity anduniform density to the body being made.

molybdenum-chromium; molybdenum-tin; molybtantalum-alu- Frequently,however, it is desired to make onlycertain parts of the body accordingto the invention, i. e. to make a composite body, such as. making acontact pin in which case only the outer contact surface is to. be hardand resistant to heat and oxidation, whilst the remaining part may nothave the same resistance capability as the contact surface. In such acase the procedure is preferably such that a mould open at the top isused, the lowest part of which is adapted to the contact surface, onwhich the higher melting metal powder is applied in sufficient layers,after which the lower melting metal is poured or fused thereon, carenaturally being taken that no air bubbles are entrained and consequentlythe casting is preferably carried out in a mould with discard head andin such a way that slow cooling which progresses from the bottom to thetop is effected. A contact is then obtained which contains the highermelting metal at the contact surface and which possesses the desiredgeneral properties.

Similar results can also be attained by choosing the metals according totheir density and taking care that the metal bath in which the lowermelting metal is fluid and the heavier high melting metal is solid,remains in the hot liquid state for a certain time, as a result of whichthe heavy metal powder can slowly move downwards and the bath is atleast enriched in heavier high melting metals or metal powders in thelower part thereof, whereupon the bath is allowed to set.

It is always possible to add the high melting metal not only in the formof ductile powder but also in other form as short or long wires whichhave been bundled or laid and which consequently have already beenrendered compact and ductile during their preparation by hammering,drawing and so forth. These bodies can then be enclosed or melted aroundby the desired lower melting metal as a result of which a composite bodyis attained from which the desired articles can be made. Thus it ispossible to cast a lower melting metal (or metal mixture) cylindricallyaround such a cable or the like of tungsten or molybdenum wire. This canbe more particularly carried out in a continuous process, such as inmachines for pressing the soft metal about the hard and thin plates, orlonger, somewhat cylindrical composite bodies which are used, as contactbodies. In these the wires of tungsten or molybdenum are thenincorporated so that the electric current advantageously flows in thedirection of the fibre of the wire.

When the composite body is made in the said manner in a machine forpressing one metal around the other, the lower melting metal is unitedto the harder metal in the hot liquid state or at least in a plasticstate produced by heating. Production is effected, therefore, both inthe hot state and under raised pressure which can be increased inindividual cases to between 25 atm. and 50 atm. and even above.

The finely crystalline structure of the composite body sets in ofitself, the higher melting metal obtained by melting or highly sinteringeither already possessing such structure or else Y acquiring itsubsequently by mechanical working.

If necessary, however, a particularly desired finely crystallinestructure may be obtained by thermal treatments such as known per se inthe metal working art. thus, for example. by rapid cooling or chillingof the composite body during the manufacture or by subsequent heating ofthe ready made article or body and subsequent rapid cooling thereof.

It is a well-known fact that the union of higher rnclting metals liketungsten and molybdenum with othcr bodies ofiers difficulties. Suchbodies of high melting point are frequently chosen since they can beheated to a higher temperature during use, and the union with a supportmust then be effected with the aid of a hard solder. As a rule whensoldering undesirable oxidation appears on the tungsten etc. body. Formany purposes also tungsten, etc., bodies are required having a compactsurface (high lustre) which offers resistance to corrosion. Such compactbodies, however, can be produced only by mechanical working, forexample, by rolling out tungsten sheets of extraordinary thinness. areshaped or cut from such sheets and united with other bodies by means ofhard solders, then merely the compact skin is lost by oxidation.

According to the invention sheets of tungsten, molybdenum and so forth,are made of the desired thickness, and also sheets of a conglomerate ofthe kind above described, e. g. of copper-tungsten, and these two sheetsare layed one upon the other and united in the hot, advantageously in areducing atmosphere and by mechanical pressure. The sheets blendtogether and a unitary sheet is obtained which consists of tungsten onone side and of copper-tungsten on the other side. However,copper-tungsten is easy to solder. In addition the tungsten on thecopper-tungsten side can be dissolved out, e. g. by etching withpotassium nitride, so that a sheet is obtained which consists oftungsten on one side and to a greater or less extent of pure copper onthe other side. The union between these two parts is extraordinarilyintimate and they cannot be separated either during subsequent workingor during operation. No perceptible electrical transition resistance canbe detected, nor is it to be expected since non-conducting oxides areabsent.

The procedure may also be such that a sheet of copper-tungsten is laidon a tungsten sheet of any desired thickness or thinness and on top ofthe same a sheet of copper is placed, and the.

three sheets are united to a three-fold sheet in the hot and in areducing atmosphere and preferably with employment of a suitablepressure. Once again the copper-tungsten is intimately and inseparablyunited both with the tungsten and with the copper. In this case thechemical treatment of the copper-tungsten for the purpose of dissolvingout the tungsten is dispensed with. This latter process is frequently ofadvantage since pores are formed in the copper owing to the dissolutionof the tungsten which are desirable for soldering purposes.

A further method consists in rolling out a block of copper-tungstenprepared as being described above and which consists for the most partof tungsten on the one side and on the other side for the most part orexclusively of copper in the direction of the layers whereby a sheet isobtained which on one side consists for themost part or exclusively oftungsten and on the other side for the most part or exclusively ofcopper. A tungsten sheet can be united with this sheet on the sideconsisting for the most part of tungsten in the manner previouslydescribed, should the sheet not be forthwith suitable for the purpose inview.

Sheets obtained in this way may be of any desired thickness or thinness;the thickness of threefold sheets can always be considerably less than 1mm. since the individual sheets can be rolled out to thicknessesamounting to a fraction of a millimetre e. g. i mm).

If electric contacts are stamped out of such a sheet then these can beunited with the support. e. g. iron or aluminum spring, by softsoldering,

If now bodies all oxidation and structural change in the joined partbeing excluded. Sheets obtained in the said way may also be coated withtin on the copper side, or a sheet of tungsten-copper-tin may be madefirst of all when the soldering is particularly facilitated andsoldering temperatures of 230 C. and less may be employed. No oxidationnor impairing of the mirror-smooth highly lustrous rolled surface of thetungsten can take place, which latter surface on account of its greatcompactness is substantially more resistant to corrosion and oxidationthan the surfaces of known contacts. If, however, as has been frequenthitherto, the contacts must be hard soldered with nickel or nickelalloys or even welded then oxidation of the tungsten-body isunavoidable, the compact rolled surface disappears and of course thecontact surface cannot be produced again even by subsequent rubbing withemery or polishing, It is obvious that by such heat treatment steelsprings or special alloys which rust only with difficulty are impaired.In addition the expedient of welding the tungsten contact on to an ironbase first of all which in turn is united with the support has, quiteapart from its cost, afiorded no permanent help.

A further advantage of the invention, however, consists in this thatcontacts can now be made from the thinnest sheet tungsten, which is madeof a thinness approaching that of a skin (about mm. thick) and united tothe support by means of soft soldering with the aid of the connectinglayer. This expedient can be adopted in all cases in which particularheating does not arise during the operation, as, for example, in thecase of telephone contacts, (more particularly for contact springs inautomatic telephony) which must not oxidise and must occupy as littlespace as possible.

Double or multi-layered sheet made in the manner described can also bepressed in an astonishing manner in the cold or under conditions ofslight heat. Obviously the thin tungsten sheet is mad more shapeable (i;e. plastic) owing to its ideal union with the still more ductilecopper-tungsten sheet. A body made in this way can then be used as suchor after removal of the copper by chemical means (dissolution in nitricacid). The tungsten skeleton remaining after dissolution of the coppercan then be rubbed down, scraped off or ground ofi. In this way it ispossible to make even complicated articles of tungsten, molybdenum andso forth, such as, for example, calottes or bodies of revolution, suchas hitherto for many purposes (Rontgen electrodes) could be made only atmuch cost and trouble by difficult casting operations.

It may be said in general that the invention enables either difficultymelting or hard bodies to be coated more particularly plated, with lowmelting or softer bodies to any desired thickness on one or both sides,or vice versa low melting or soft bodies to be coated or plated withhigher melting or harder bodies on one or both sides. The union is inevery case effected in the heat with suitable mechanical pressure andabsence of oxidising agents.

The invention is not in any way limited to the procedure set forth inthe examples given, It may be used, for example, for loom motor switcheswhich as is well known are subjected to a very great mechanical Wear.The contact of such a switch has approximately a double T-cross sectionand according to the invention is made for the most part from a copperrod which is provided on one side with a layer of coppertungsten and isthen drawn or rolled into the desired section, so that a copper rail isobtained which has one surface of copper-tungsten and from which acontact of the desired length can be cut ofi. In a similar way, fromround copper rods which are coated completely with a coppertungstenlayer it is possible to draw tubes or wires which consist on theexterior of coppertungsten and in the interior of copper.

Although here conglomerate bodies of any desired shapes, such as wires,and sheet, consisting of tungsten and copper have been more particularlydescribed, yet the process may be employed to every other conglomeratebody such as has been set forth in the introduction. Thus, for manypurposes aluminum bodies with tungsten or molybdenum layers, as well ascopper bodies with tungsten layers, are to be recommended.

What I claim is:

1. An agglomerated material, in particular for electrical purposes, andshaped bodies made therefrom, consisting of at least one metal selectedfrom a first group consisting of tungsten, molybdenum and tantalum, andat least one metal selected from a second group consisting of silver,nickel, cobalt, iron, copper, aluminum, gold, chromium, tin, zinc,platinum, the metal of said first group present in individual denseparticles coarser than those of the original metal powder obta ned fromits compounds or ores, and obtained in such coarser state by heattreatment at temperatures at least as high as sintering temperature andsubsequent powdering, the metal of said second group formingsubstantially a solidified melt agglomerating said individual coarseparticles and present in amounts of about 3% to of the material orbodies.

2. An agglomerated material, in particular for electrical purposes, andshaped bodies made therefrom, cons sting of at least one metal selectedfrom a first group consisting of tungsten, molybdenum and tantalum, andat least one metal selected from a second group consisting of silver,nickel, cobalt, iron, copper, aluminum, gold, chromium, tin, zinc,platinum, the metal of said first group present in a fibrous statecomminuted to dense particles coarser than those of the original metalpowder obtained from its compounds or ores, the metal of said secondgroup forming substantially a solidified melt agglomerating saidparticles and present in amounts of about 3% to 90% of the finalmaterial or bodies.

3. An agglomerated material, in particular for electrical purposes, andshaped bodies made therefrom, conssting of at least one metal selectedfrom a first group consisting of tungsten, molybdenum and tantalum, andat least one metal selected from a second group consisting .of silver,nickel, cobalt, iron, copper, aluminum,

gold, chromium, tin, zinc, platinum, and an admixture of titanium in anamount of about 3% to 15%, the metal of said first group present inparticles coarser than those of the original metal powder obtained fromits compounds or ores, the metal of said second group formingsubstantially a solidified melt agglomerating said particles, containingsaid admixture and being present in amounts, including said admixture,of about 6% to 90% of the final material or bodies.

4. A process of manufacturing an agglomerated material for electricalpurposes and shaped bodies therefrom, containing at least one metalselected from a first group consisting of tungsten,

molybdenum, tantalum, and at least one metal selected from a secondgroup consisting of copper, aluminum, gold, chromium, tin, zinc,platinum, said process consisting in first compacting metal taken fromsaid first group in its initial powdery form in which it is obtainedfrom its compounds or ores by heat treatment at temperatures at least ashigh as sintering temperature, then powdering the so compacted metal toparticles coarser than those of the initial powder and mixing it withmetal taken from said second group, and thereupon consolidating thismixture by heat treatment at temperatures below the sinteringtemperature of said first group metal. 7

5. A process of manufacturing an agglomerated material for electricalpurposes and shaped bodies therefrom, containing at least one metalselected from a first group consisting of tungsten, molybdenum andtantalum and at least one metal selected from a second group consistingof cobalt, iron, aluminum, gold, chromium, nickel, tin, zinc,

platinum, said process consisting in first compacting by heat treatmentinitial metal taken from said first group in the powdered form in whichit is obtained from its compounds or ores at temgg peratures at least ashigh as sintering temperature, then mechanically working the compactedmetal, then powdering the so compacted metal to particles coarser thanthose of the initial powder and mixing it with metal taken from saidsecond group, thereupon heating this mixture at a temperature at leastsufiiciently high to melt the metal taken from said second group butbelow a temperature at which the structure of the metal of said firstgroup is materially changed.

6. A process of manufacturing an agglomerated material for electricalpurposes and shaped bodies therefrom, containing at least one metalselected from a first group consisting of tungsten, molybdenum,tantalum, and at least one metal selected from a second group consistingof silver, nickel, cobalt, iron, copper, gold, aluminum, tin, zinc,chromium, platinum, and an admixture of titanium in an amount of about3% to 15%, said process consisting in first compacting metal taken fromsaid first group in its initial powdery form in which it is obtainedfrom its compounds or ores by heat treatment at temperatures at least ashigh as sintering temperature, then powdering the so compacted metal toparticles coarser than those of the initial powder and mixing it withmetal taken from said second group and said admixture, and thereuponconsolidating this mixture by heat treatment at temperatures below thesintering temperature of said first group metal.

7. A process of manufacturing agglomerated shaped bodies for electricalpurposes containing at least one metal selected from the first groupconsisting of tungsten, molybdenum, tantalum, and at least one metalselected from a second group, consisting of silver, nickel, cobalt,iron, aluminum, gold, chromium, tin, zinc, platinum, said process conssting in first compacting metal taken from said first group in itsinitial powdery form in which it is obtained from its compounds or oresby heat treatment, at temperatures at least as high as sinteringtemperature, then powdering the so compacted metal to particles coarserthan those of the initial powder, shaping the powder formed of saidparticles and thereupon pouring thereover melted metal taken from thesecond group, and cooling the agglomerated body thus obtained.

PAUL SCHWARZKOPF.

